Heat shock protein 70 vaccination induced immune responses in bovine paratuberculosis

Abstract

Mycobacteriun avium ssp. paratuberculosis (MAP) is the pathogen that causes paratuberculosis in ruminants worldwide. In Western Europe and the USA it affects up to 30% of cattle herds. In the subclinical stage of paratuberculosis production losses occur and the bacterium is shedded into the environment. In a minority of animals the disease ultimately progresses into a fatal protein loosing enteropathy. To date no vaccine is available for paratuberculosis in cattle Heat shock proteins (Hsp) are evolutionary conserved molecules that have shown to be immunogenic in different stages of bovine paratuberculosis. After natural or experimental infection immune responses to (MAP) Hsp70 protein, predicted to be protective, were predominantly cell mediated. Efficacy of vaccination with MAP Hsp70 using DDA as an adjuvant was studied in a longitudinal study with vaccinated and experimentally infected animals and relevant controls. Immune responses and bacterial shedding were measured for almost 2 years. Single priming of the animals induced an immune response, which clearly differed from that after encounter of the protein during infection. MAP Hsp70 induced IFN-? production was observed in this study, however this was related to the infectious challenge rather than to vaccination. A prominent and prolonged production of antibodies to MAP Hsp70 was restricted to the immunized groups. It correlated well with the observed significantly reduced shedding of bacteria in the immmunized and challenged group, suggesting a role for antibodies in protection. The clear divergence/discrepancy observed in antibody production enables differentiation between vaccinated and non-vaccinated animals even within infected herds which may clearly be an advantage in the application of the MAP Hsp70 vaccine. The use of subunit vaccines implies reduction of MAP specific epitopes hence fine specificity of T- and B cell responses were studied in outbred animals. Th1 cell responses studied in MAP Hsp70 immunized animals identified specificity for 9 epitopes, and part of the epitopes proved to be promiscuous as responses to individual epitopes were detected in up to 82% of the animals (15 different MHC haplotypes) experimentally infected with MAP. Based on recognition by MAP Hsp70 specific monoclonal antibodies and epitope mapping using synthetic peptides of MAP Hsp70 at least two linear B cell epitopes were identified, which were recognised in vaccinated outbred calves and goats as well. This study also provided indications that the Hsp70 protein is present in the bacterial cell wall of MAP and it may be argued that antibodies, induced by vaccination, may bind intact bacteria and play a direct role in the protective effect.. In the course of paratuberculosis and potentially in protection after vaccination regulatory T-cells are likely to play a role. Our studies provided first evidence that cattle CD4+CD25high and CD4+CD25low T cells do not function as regulatory T cells (Treg) The bovine regulatory cell function, as defined by ex vivo suppressive capacity appears to reside in CD14+ monocytes and in the ?? T cell population, major populations present in blood of cattle in contrast to non-ruminant species. The exact mechanism of the suppression observed and Ag specific regulation (MAP Hsp70) has to be addressed in future studies.